TD render fix 2: Electric boogaloo

This fixes TD's terminal stage freezing the game in a similar manner to Lava Mountain, except this time the FOFs aren't zero-height so it's a slightly different situation?

src/r_segs.c

@@ -708,7 +708,10 @@ static void R_DrawRepeatMaskedColumn(column_t *col)
{
while (sprtopscreen < sprbotscreen) {
R_DrawMaskedColumn(col);
-		sprtopscreen += dc_texheight*spryscale;
+		if ((INT64)sprtopscreen + dc_texheight*spryscale > (INT64)INT32_MAX) // prevent overflow
+			sprtopscreen = INT32_MAX;
+		else
+			sprtopscreen += dc_texheight*spryscale;
}
}